DC arc furnaces having electrically conductive hearths are disclosed by U.S. Pat. Nos. 4,228,314 and 4,324,943.
The hearth of such a furnace is adapted to contain a melt of molten metal, the furnace having at least one arcing electrode with a tip positioned above the hearth and adapted to form a heating arc with the melt when the electrode and hearth are supplied with DC power.
In the patents, the hearth comprises a wear lining directly contacted by the melt and formed by refractory material through which electrical conductors extend from the bottom of the wear lining to the top for contact with the melt. Superimposed layers of electrically conductive bricks are laid beneath the wear lining and connect the bottom portions of the conductors with a metal conductor plate below and in electrical connection with the bottom layer of the electrically conductive bricks. The metal plate is adapted to be connected with the DC power circuit including the arcing electrode.
In U.S. Pat. No. 4,228,314 the refractory material through which the electrical conductors extend is formed by a refractory compound rammed on the conductive bricks with the conductors formed by metal rods extended through the compound. In U.S. Pat. No. 4,324,943 the refractory compound is formed by bricks through which the electrical conductors extend, or metal encased bricks may be used.
The electrical conductors used with either of the refractory materials, rammed compound or bricks, the electrically conductive bricks and the metal plate, are not only good electrical conductors as required for the arc's power circuit but are also correspondingly good thermal conductors. Consequently the heat of the melt heated by the arc is to a high degree transmitted to the metal plate. This can result in excessive heating of the metal plate and therefore the furnace bottom.